Electrostatic liquid developer containing dye coated carbon particles

ABSTRACT

NEW AND IMPROVED TONER PARTICLES FOR USE IN A LIQUID DEVELOPING COMPOSITION FOR CONVERTING A LATENT ELECTROSTATIC IMAGE TO A VISIBLE IMAGE AND METHOD FOR THEIR PREPATATION WHEREIN CARBON PIGMENT MATERIAL IS TREATED WITH A DYE CARRYING A POSITIVE ELECTROSTATIC CHARGE DISSOLVED IN A POLAR ORGANIC SOLVENT.

United States Patent U.S. Cl. 252 -621 3 Claims ABSTRACT OF THEDISCLOSURE New and improved toner particles for use in a liquiddeveloping composition for converting a latent electrostatic image to avisible image and method for their preparation wherein carbon pigmentmaterial is treated with a dye carrying a positive electrostatic chargedissolved in a polar organic solvent.

This invention relates to electrostatic printing, and more particularlyto a method for treating pigment or toner particles for use in liquiddeveloping compositions for converting an electrostatic image to avisible image.

Processes for forming a latent electrostatic image, existing as anelectrostatic charge pattern in a layer of material having highresistance, and for subsequently converting the latent electrostaticimage into a visual pattern, are well known.

In one such process, an optical image is produced directly on a film orcoating of a photoconductive pigment, such as zinc oxide dispersed in aninsulating matrix, such as a synthetic resin, on the surface of aflexible carrier, such as a sheet of paper, metal or other electricallyconductive backing. In this process, the photoelectrostatic coating isgiven an overall electrostatic charge while being protected from lightand thereafter it is exposed to a light image of the subject to bereproduced. The electrostatic charge on the coating is dissipated in theareas struck by light and retained in the unexposed areas thereby toprovide an electrostatic reproduction of the optical image. This latentelectrostatic image is then converted to a visible image by a developingcomposition containing toner particles which are attracted to the latentelectrostatic image in a positive toning process, or to the backgroundarea in a negative toning process.

In another process referred to as the Videograph process described inU.S. Pats. No. 2,996,573 and No. 3,075,859, a latent electrostatic imageis inscribed by elements extending through a cathode ray tube directlyonto the dielectric coating on the surface of a base sheet of paper orother highly electrically conductive material. The latent electrostaticimage is retained on the dielectric coating and later developed into avisible image by the application of a suitable developing compositioncontaining toner particles which are attracted to the latentelectrostatic image or the background, as described above.

Liquid developer compositions for use with electrostatic images comprisea dispersion of a pigment or toner particles in a volatile liquid havinga high dielectric strength and a high volume resistivity. The dispersedparticles may carry either a positive charge or a negative electricalcharge, depending on their chemical composition for either positivetoning or negative toning respectively. The nonconductivity and the highdielectric strength of the volatile liquid in the liquid developingcomposition preserves the electrostatic image and permits the depositionof the dispersed toner particles to form a visible image. Liquid tonersare described in the U.S. Metcalfe Pat. No. 2,907,- 674, the U.S.Straughan Pat. No. 2,899,335, the U.S. Mayer et al. Pat. No. 2,390,911,the U.S. York Pat. No.

3,135,095 and the U.S. Dirks Pat. No. 3,155,546, and many others.

Although liquid developing composition represent an improvement over theuse of earlier dry powder developers used for conversion of a latentelectrostatic image to a visible image, improvement of the liquiddeveloping compositions is desirable from the standpoint of producingpermanent visible images which are free from smearing or blurring,especially when rubbed. This deficiency stems from the inability of thetoner particles to become permanently fixed on the surface of the copysheet. In addition, liquid developing composition heretofore known havethe further disadvantage in that the pigment or toner particlescontained therein have a tendency to agglomerate, whereby destroying thedispersion of the toner particles in the liquid developing composition.

Attempts have been made to overcome these disadvantages and to fix theimage onto the copy sheet by subsequent processing, as by heating tofuse the toner particles, but such additional processing steps are oftenincomplete. Moreover, attempts to provide a more complete v dispersionof the toner particles in the liquid developing composition have beenmade, but have similarly been ditficult to achieve.

It is accordingly an object of the present invention to provide new andimproved toner particles and method for preparing same wherein the tonerparticles become permanently fixed to the copy sheet to provide a dense,black image of good resolution on development of the latentelectrostatic image.

It is a further object of the present invention to provide a method fortreating toner particles whereby the individual toner particles arecaused to repel each other to thereby prevent agglomeration of the tonerparticles over long periods of time.

It is a related object of the present invention to provide new andimproved toner particles and a liquid developing composition embodyingsame for converting an latent electrostatic image to a visible imagewhich provides a clean background on the copy sheet, which promotes goodadherenec of the toner particles to the copy sheet to prevent streakingand smearing of the visible images, and which will promote the uniformdevelopment of a dense, black image.

The concepts of the present invention reside in a method for treatingtoner or pigment particles wherein a carbon pigment material is treatedwith an organic solvent containing a dye which carries a positiveelectrostatic charge. It has been found that pigment material treated inthis manner provides an increased image intensity, and completelyobviates the problem of agglomeration of the toner particles in thedeveloping composition. Without limiting the invention as to theory, itis believed that the method of the present invention causes the carbonpigment material, which inherently carries a negative electrostaticcharge, to become coated with a layer of the dye which carries an activepositive electrostatic charge. Thus, the complete absence ofagglomeration of toner particles formed of the treated pigment materialsis believed to result from the repulsion of the actively positivelycharged toner particles.

In accordance with the practice of the present invention, a dye whichcarries a strong positive electrostatic charge is dissolved in a polarorganic solvent, and the resulting solution is used to treat the carbonpigment material. The solid carbon pigment material is then sep aratedfrom the liquid phase, dried and powdered, and formulated into a liquidtoner concentrate and/or liquid toner developing composition.

In accordance with the preferred practice of the invention, afterseparation of the liquid phase containing M the polar organic solventand dissolved dye, the separated liquid phase is either combined with asecond organic solvent, and the resulting mixture used to wash thesolids comprising the treated carbon pigment material, or the solidcarbon pigment material is treated with the second solvent alone and theliquid phase containing the second solvent, which is thereafterseparated from the solid carbon pigment material, is mixed with theliquid phase from the first treatment to provide an additional treatingmedium for the solid carbon pigment material. Thereafter, the treatedpigment material can be formulated into a liquid developing compositionfor converting a latent electrostatic image to a visible image.

A variety of carbon pigment materials may be used in the practice of thepresent invention, including carbon black, lamp black, channel black orthe like. It is generally preferred to make use of carbon blacks, suchas Mogul A, Raven 11 or GAF permanent black toner 84-5001.

Similarly, a wide variety of dyes may be used in the treatment of theforegoing carbon materials, with the primary requirement of such dyesbeing that they must carry a strong positive electrostatic charge.Nigrosine dyes, such as Nigrosine Base B or Nigrosine Base SSB (0.1.50415), are frequently preferred, although use may also be made of otherdyes which carry a positive electrostatic charge, such as methyl violet(CI. 42435) or alkali blue dyes (e.g. Alkali Blue R Powder 55-4570 (CI.42750), marketed by American Cyanamide).

The polar organic solvent used in accordance with the practice of thepresent invention should be a solvent for the dye. For this purpose, usecan be made of aliphatic alcohols having 1-5 carbon atoms, such asmethanol, ethanol, isopropanol, etc., or aliphatic ketones having 3-10carbon atoms, such as acetone, methyl ethyl ketone, diethyl ketone,ethyl propyl ketone, etc. Separation of the solvent from the treatedcarbon material can be etfected by a variety of conventional procedures,although it is generally preferred to filter the mixture of the carbonmaterial with the solvent containing the dissolved dye in order toseparate the solid pigment material from the dyecontaining solvent. Itwill be understood that various other means of separation, such ascentrifugation may similarly be used.

The second solvent, which may be either combined with the liquid phasecontaining the polar organic solvent resulting from the initialtreatment, or used as a treating medium alone and thereafter combinedafter separation of the pigment material with the liquid component ofthe initial treatment to provide a third treating medium can be either apolar or non-polar organic solvent. For example, use can be made ofpolar solvents of the type described above, such as methanol or methylethyl ketone, or non-polar aromatic and cycloaliphatic hydrocarbonsolvents, such as benzene, toluene, xylene, cyclopentane, cyclohexane,etc. It will be appreciated by those skilled in the art that mixtures ofthe foregoing polar or non-polar solvents may be used to provide asecond solvent in accordance with this invention.

When both the polar and the second solvent are used in accordance withthe preferred embodiment wherein the second solvent serves as anadditional treating medium, it has been found that best results areobtained when the polar solvent is ethyl alcohol and the second solventis an aliphatic ketone of the type described above, such as methyl ethylketone. Pigment material treated with this solvent system providesparticularly well defined dark images when formulated into a liquiddeveloper composition for converting latent electrostatic images tovisible images.

Having described the basic concepts of this invention, reference is nowmade to the following examples which are provided by way ofillustration, and not by way of limitation, of the method for treatmentof pigment material in accordance with the practice of this invention.

4 EXAMPLE 1 A sample of 20 grams of a nigrosine dye (Nigrosine SSB) isdissolved in 200 ml. of ethanol, and then 40 grams of carbon black(Mogul A) are added. The resulting mixture is then vigorously agitatedand filtered. The resulting filtrate is then dried and powdered.

EXAMPLE 2 The procedure of Example 1 is repeated except that the solventemployed is methyl ethyl ketone.

EXAMPLE 3 Six grams of carbon black are admixed with one gram ofnigrosine dye (Nigrosine SSB) and dissolved in 200 ml. of ethyl alcohol.The resulting mixture is then filtered, and the ethyl alcohol filtrateis used to wash the filter cake. Thereafter, the filter cake is washedwith methyl ethyl ketone, and the ketone filtrate is combined with thealcohol filtrate from the first washing are admixed and used to wash thefilter cake again.

The filter cake resulting from the third washing is then dried andpowdered in the manner described in Example 1.

EXAMPLE 4 The procedure of Example 3 is repeated except that the ethylalcohol solvent is replaced by methyl ethyl ketone and the methyl ethylketone solvent is replaced by benzene.

EXAMPLE 5 The procedure of Example 3 is again repeated except that themethyl ethyl ketone solvent is replaced by cyclohexane.

EXAMPLE 6 The procedure of Example 3 is again repeated except that theethyl alcohol solvent is replaced by methyl alcohol, and the ketonesolvent is replaced by toluene.

EXAMPLE 7 Twenty grams of nigrosine dye (Nigrosine Base B) are dissolvedin 200 ml. of ethyl alcohol, and 40 grams of carbon black are added tothe mixture. Thereafter, the mixture is filtered, and the filtrate isadmixed with ml. of methyl ethyl ketone. The resulting mixture is thenused to wash the filter cake, which is then dried and powdered.

EXAMPLE 8 The procedure of Example 7 is repeated except that the methylethyl ketone solvent is replaced by toluene.

EXAMPLE 9 The procedure of Example 7 is again repeated except that themethyl ethyl ketone solvent is replaced by cyclohexane.

EXAMPLE 10 Ten grams of alkali blue powder (Alkali Blue R powder55-4570) are dissolved in 150 ml. of ethyl alcohol, and 25 grams ofcarbon black are added to the solution. The resulting mixture is thenfiltered, and the filter cake is Washed with the filtrate. Thereafter,the filter cake is washed with methyl ethyl ketone, and the ketonewashing liquid is combined with the filtrate from the first wash andused to again wash the filter cake. The resulting treated tonerparticles are dried and powdered.

EXAMPLE 11 The procedure utilized in Example 10 is repeated except thatthe ethyl alcohol solvent is replaced by methyl ethyl ketone and themethyl ethyl ketone solvent is replaced by benzene.

EXAMPLE 12 The procedure of Example 10 is again repeated except that themethyl ethyl ketone solvent is replaced by cyclopentane.

EXAMPLE 13 Five grams of the alkali blue dye utilized in Example aredissolved in 150 ml. of methyl alcohol, and 20 grams of carbon black areadded to the solution. The resulting mixture is then filtered and thefilter cake is washed with 100 ml. of toluene. Thereafter, thealcoholcontaining filtrate and the toluene filtrate are combined, andthe mixture used to wash the filter cake again.

The treated carbon black filter cake is then dried and powdered.

EXAMPLE 14 The procedure used in Example 13 is repeated except that thetoluene solvent is replaced by methyl ethyl ketone.

Toner particles which have been treated in accordance with the presentinvention as illustrated b Examples 1 to 14 may be formulated into avariety of liquid developer compositions used for converting a latentelectrostatic image to a visible image. For example, toner or pigmentparticles of the present invention may be used in a liquid developer ofthe type disclosed in the Metcalfe patent (US. No. 2,907,674), whichgenerally comprises the pigment or toner particles and a bindercomponent dispersed in an organic solvent which functions as a carrier.Such a developer composition is illustrated by the following example.

EXAMPLE A developer concentrate is prepared by admixing 5 parts byweight of the toner particles prepared in accordance with Example 1 with7 parts by weight of a lineseed oil-modified alkyd resin (RhodeneL6/100) binder and 15 parts by weight of a high boiling aromatic solvent(Fusis A), and ball milling the mixture for several hours to insure andprovide the toner concentrate:

Parts by wt. Treated carobn black particles 5 Alkyd resin 7 Aromaticsolvent 15 The toner concentrate can then be dispersed in a carriersolvent, such as cyclohexane, carbon tetrachloride or the like toprovide a toner particles content which may be varied within wideranges, such as from 0.00001 to 5% by weight of the developercomposition.

It will be understood that a wide variety of binder components may beused in lieu of the alkyd resin exemplified in Example 15, the primaryrequirement being that the binder component have a relatively highdielectric constant. Illustrative of suitable binders are polyvinylacetate, polyvinyl acetate copolymers containing carboxyl groups (egsuch as VMCH resin (marketed by Union Carbide which comprisesapproximately 86% by weight vinyl chloride, 13% by weight vinyl acetateand 1% by weight maleic acid), polyvinyl chloride, polyvinyl acetatecopolymers, polystyrene, styrene-butadiene copolymers, alkyd andmodified alkyd resins, polyvinyl toluene, such as Pliolite VTL marketedby Goodyear. The binder components of the developing composition aregenerally insoluble in aliphatic solvents which serve as the carrier forthe toner concentrate, and hence it is generally preferred to dissolvethe binder component in a small amount of a aromatic solvent, such asNapoleon 100-A marketed by the Deeprock Division of Kerr-McGee Company,and then disperse the dissolved binder in an aliphatic solvent in orderto provide a fine dispersion of the binder particles in the aliphaticsolvent carrier system. The binder is generally present in thedeveloping composition in an amount within the range of 0.001 to 10% byweight.

As indicated, the compatible carrier system for use in admixture withthe toner concentrate to provide the developing composition generallycomprises an aliphatic solvent, and preferably a solvent having a highvolume resistivity in exces of 10 ohm-cm. so as to avoid dissipation ofthe charge in the latent electrostatic image. For

this purpose, use can be made of aliphatic solvents, such ascyclohexane, carbon tetrachloride, Isopar H, which is an aliphaticsolvent marketed by the Humble Oil & Refining Company having a flashpoint of 123 F., Isopar G, also marketed by Humble, having a flash pointof 104 F. The Isopar solvents both have a KB value of 27 and a low odorlevel. In formualting the liquid developing composition, it is generallydesirable to employ between 0.001 and 5 parts by weight of the tonerconcentrate per parts by weight of the carrier system so as to provide aliquid developing composition containing the toner particles in anamount corresponding to 0.0001 to about 1.0% by weight of the developercomposition.

The new and improved toner particles of the present invention may alsobe used in the developer concentrates and compositions of the typedisclosed in copending application Ser. No. 818, filed J an. 5, 1970,and entitled Liquid Developer Composition, wherein description is madeof a toner concentrate containing toner particles suspended in anorganic solvent by means of rosin and derivatives thereof which isadapted to be combined with a compatible carrier system formulated tocontain a binder capable of forming a dielectric film to thereby anchorthe pigment particles to the copy sheet during the development of alatent electrostatic image. Such developer concentrates and compositionsmay be formulated in accordance with the following examples.

EXAMPLE l6 Ethyl alcohol (40 grams) is mixed with 20 grams of a mixtureof flushed toning blue dissolved in mineral oil and an aliphatic solvent(Isopar G), and the resulting mixture is osterized for four minutes.Thereafter, this flushed blue toning mixture is formulated into thefollowing toner concentrate utilizing pigment particles treated inaccordance with Example 1:

Treated carbon black 5.0 Hydrogenated methyl ester of rosin (Hercolyn D)50.0

Rosin oil (Rosin Oil 6R8) 5.0

Isobutylene polymers (Paratone 460) 5.0

Flushed blue toner mixture 5.0

Aliphatic solvent 15.0

The foregoing toner concentrate is thoroughly mixed by ball milling forseveral hours.

As used in the aforementioned application, the term rosin is meant torefer to rosin and derivatives thereof, as well as mixtures of variousrosins. Included are tall oils of rosin and decarboxylated rosin oils(e.g. Rosin Oil 6R5) and ester and hydrogenated ester derivatives oftall oils of rosin.

The toner concentrates described above are preferably formulated toinclude a fixing agent in the form of polymers of isobutylene whichoperates at least in part to aid in anchoring the pigment particles tothe copy sheet during development of the electrostatic image. Thesolvent which is included in the toner concentrate to maintain thepigment particles is dispersion or suspension is preferabl-y a solventhaving a high volume resistivity as de scribed above.

The relative proportions of the components in the concentrate anddeveloper compositions are not critical and can be varied within wideranges. For best results, it is generally desirable that the concentratebe formulated to include between 10 and 60% by weight of the rosin, upto 10% by weight of the isobutylene polymers, and from .01 to 10% byweight of the treated pigment or toner particles.

It will be appreciated by those skilled in the art that the flushed bluetoning component described above may be omitted from the composition asillustrated by the following example, in which use is made of thepigment particles treated in Example 3.

7 EXAMPLE 17 A toner concentrate is prepared by thoroughly mixing thefollowing compositions in a ball mill:

Treated carbon black 50.0 Hydrogenated methyl ester of rosin (HercolynD) 50.0 Isobutylene polymers (Paratone 460) 5.0 Rosin oil (Rosin Oil6R8) 5.0 Aliphatic solvent 20.0

The toner concentrates of Examples 16 and 17 may be admixed with acompatible carrier system containing a film forming binder which servesin part to anchor the pigment particles to the copy sheet upon drying.The carrier compositions may be illustrated by the following example.

EXAMPLE 18 The concentrates of Examples 16 and 17 can be added to theabove carrier composition to provide a liquid developing compositionhaving a pigment content of 0.00002 to 0.01% by weight. The relativeproportions of concentrate and carrier used may be varied between wideranges. Best results are obtained when the concentrate is added to thecarrier in a ratio of .1 to 10 parts by weight concentrate to 1000 partsby Weight of the carrier.

It will be appreciated that any of the binders discussed above withreference to Example 15 may be used in place of the polyvinyl tolueneexemplified in Example 18.

In use, the copy sheet containing the latent electrostatic image is wetwith the liquid developing composition, with the immersion of the sheetin a bath of the developing composition or by flow-coating thecomposition over the image surface or by application of the liquiddeveloping composition onto the image surface by a roller-coater. Thecopy sheet which is wet with the developing composition is then advancedthrough squeeze rolls to remove excess liquid. The toner particles areattracted to the latent electrostatic image for visual development ofthe image on the copy sheet. After development, the copy is allowed todry by evaporation of the liquid, with or without the application ofheat. The aliphatic solvents evaporate from the sheet to thereby reducethe binder and the rosin to a tackified or adhesive stage whereby thedeposited toner particles become bonded to the underlying coating so asto become permanently fixed on the copy upon complete drying of thesheet.

It will be apparent from the foregoing that we have provided new andimproved pigment material for use in liquid developing compositions anda simple method for preparing same, wherein the resulting pigmentparticles formed of the pigment material are completely free fromagglomeration and which provide a well defined image on a cleanbackground.

It will be understood that various changes and modifications may be madein the details of formulation, procednre and use without departing fromthe spirit of the invention, especially as defined in the followingclaims.

We claim:

1. In a liquid developer composition for converting a latentelectrostatic image to a visible image comprising a binder and tonerparticles suspended in an organic solvent having a volume resistivity inexcess of 10 ohmcm., the improvement comprising toner particles formedof carbon pigment particles which have been coated with a nigrosine dye(CI 50415).

2. A composition as defined in claim 1 wherein said pigment particlesare selected from the group consisting of carbon black, lamp black andchannel black.

3. A composition as defined in claim 1 wherein said pigment material iscarbon black.

References Cited UNITED STATES PATENTS 3,325,409 6/1967 Whitbread25262.1 3,290,251 12/1966 Nelson 252-62.1 3,220,830 11/1965 Kashiwabara252-62.1 3,073,231 2/1963 Metcalf et al. 25262.1 2,878,135 3/1969 Willis106-307 2,785,079 3/1957 Voet et al 106307 2,121,535 6/1938 Amon 106-3072,118,512 5/1938 Huchs 106307 2,004,514 6/1935 Battle 106307 1,730,38910/1929 Snelling 106-307 GEORGE F. LESME'S, Primary Examiner J. P.BRAMMER, Assistant Examiner U.S. Cl. X.R.

. I WUNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Pa tent No.3,7 9,670 Dated July 31, 1-973 Inventofl's) Mary K. ORMSBEE', Mouin r.SAADEH and Leonard SKUBY It'is eerti fied that error appears in theabove-identified patent and that said Letters Patent are herebycorrected as shown below:

Column 1, line 5; please delete "Skulby" and insert therefor SkfibySigned and sealed this 9th day of April 197M.

(SEAL) Attest:

EDWARD IVLFLETCHERJRQ CLMARSHALL DANN Atte sting Officer Commissioner ofPatents

